Birth and early history of carbon nanotubes (page 2 of 5)

The natural carbon nanotubes contain many particles embedded within and stripes were observed, which were attributed to the presence of other elements. The Raman spectral studies showed that the spectral signatures of naturally occurring CNTs resembled to that of commercially available multiwalled carbon nanotubes.

In yet another study, researchers from Germany11 have synthesized carbon nanotubes using igneous rock from Mount Etna lava as both support and catalyst. The naturally occurring iron oxide particles present in Etna lava rock make it an ideal material for growing and immobilizing nanocarbons.

When a mixture of ethylene and hydrogen were passed over the pulverized rocks reduced in a hydrogen atmosphere at 700°C, the iron particles catalyzed the decomposition of ethylene to elemental carbon, which gets deposited on the lava rock in the form of tiny tubes and fibers.

This study showed that if a carbon source is available, CNTs/CNFs can grow on a mineral at moderate temperatures, which directs towards the possibilities of carbon nanotube formation in active suboceanic volcanos or even in interstellar space where methane, atomic hydrogen, carbon oxides, and metallic iron are present.

CNTs as 21st century advanced material was further preempted by another significant finding by Peter Paufler and colleagues at Dresden's Technical University12. Amazingly, the electron microscopy studies conducted by them on the legendary medieval Damascus sword dating back as far as 900 AD unraveled the presence of CNTs in the microstructure of wootz steel that was used for fabricating the swords. Initial studies conducted on Damascus steel sword showed the presence of nanowires of cementite (Fe3C), a hard and brittle compound formed by iron and carbon of the steel. The CNTs were revealed only when a piece of sword was exposed to hydrochloric acid, which dissolved the microstructure made of cementite nanowires.

The carbon nanotubes encapsulated cementite nanowire bundles present in the bulk matrix of wootz steel are envisaged to be responsible for the unique properties such as extraordinary high strength and ductility as well as the characteristic banding pattern of Damascus sabre. It is believed that transition metal impurities present in the wootz iron ore, origin of which is considered to be South India, could have catalyzed the growth of nanotubes from the carbon derived from the wood and leaves used during the production of the steel.

A research group from USA has really produced CNTs from wood fiber using a low temperature process, which included continuous oxidization at 240°C and cyclic oxidation at 400°C13. The research suggested that the chemical components in the secondary plant cell wall and their differential ablation properties are critical for the formation of CNTs at these comparatively low temperatures. This study in a way supports the revelation of CNTs in wootz steel.

The issue of the natural occurrence of carbon nanotubes is currently being hotly debated since it has legal implications concerning the carbon nanotube IP regime.